History of the Related Art
Many manufacturing and material processing operations involve carrying out various procedures on a segment of a continuous film or sheet. For example, polyimide tapes or webs are typically used as the dielectric layer in multi-layered substrates for electronic circuits. In this application, holes are punched through the polyimide film to provide vias through the film for the purpose of providing electrical communication between conductive layers separated by the film. Typically, in this application, the punched holes are required to be located within 10 .mu.m (0.0005 in.) of any specified position. The punching operation may be carried in a move-stop-punch mode (MSP) or in a punch-on-the-fly X direction mode (POFX), or a punch-on-the-fly Y direction mode (POFY). When in the MSP mode, an X-Y translation table on which the punch and die assembly is supported, stops at the position to be punched before the punch actuator has fired. During the POFX and POFY modes, the X-Y table is in motion during punch actuator firing. In all three modes, the substrate is maintained at a stationery position. In the POFX and POFY modes, the relative velocity of the punch with respect to the film substrate is very significant. Hole quality requirements, i.e., the absence of tearing or adverse distortion of the hole size and shape, limit the punch and die assembly velocity with respect to the film. Distortion of the punched holes is a function of punch engagement time and the relative velocity (X-Y) between the punch and film. Distortion is also a function of the elastic properties of the film, the resiliency of the mounting or clamping system and the distance between clamping stations.
Heretofore, satisfactory hole quality, without adverse distortion, when punching holes in a thin polyimide film has been achievable at punch-die table speeds of up to about 10 mm/sec for POFX punching using rigid piston actuated clamps positioned in close proximity to the punch table. At higher velocities, hole quality becomes unacceptable. Since a large number of holes are generally punched in a specified pattern in each designated area of the continuous film, the limitation on punch table velocity with respect to the film imposes an undesirable limitation on the time required to process each designated area of the film.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a clamping mechanism which will enable higher relative velocities and higher tool productivity. It is also desirable to have such a clamping mechanism that if desired, will compliantly maintain a preselected area of the continuous film at a preselected position. It is also desirable to have such a clamping arrangement that, when the film is being transported, supports the film on an air cushion as it passes through the clamping stations. Furthermore, it is desirable to have such a transport and clamping system that is capable of selectively resiliently and compliantly holding a designated film area at a desired position at the work station, or alternatively, rigidly clamping the film structure.